Security Thread Authenticity Check Using Combined Light Profiles
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Solution Overview
Problem
Existing methods for checking the authenticity of security elements with optically variable effects, such as security threads, require different sensors and high optical resolution due to varying illumination and detection angles, making them complex and inefficient.
Innovation Solution
A method and device that detect the reversed light-dark modulation in transmission and remission images of security elements with microlenses, using a single sensor to generate intensity profiles along the security element's longitudinal direction, allowing for a simple and reliable authenticity check by evaluating the intensity modulation of the combination profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If different illumination and detection angles are used to check optically variable security threads, then the authenticity checking reliability is improved, but the device complexity increases due to requiring different sensors for different security threads
Solution Approach 1:
The patent makes a single sensor capable of performing multiple functions by implementing both transmission and remission detection modes within one sensor device. This universal sensor can check security elements with different microlens grids without requiring separate sensors for each angle of incidence, thereby reducing device complexity while maintaining the ability to detect optically variable effects
Solution Approach 2:
The patent transitions from checking only transmission images to utilizing both transmission and remission dimensions simultaneously. By evaluating the sum of difference values from both transmission and remission images, the system achieves reliable authenticity verification without requiring multiple sensors at different angles, thus resolving the contradiction between reliability and device complexity
2Measurement precision
If high optical resolution is used to recognize motifs in security threads, then the measurement precision is improved, but the device complexity and cost increase
Solution Approach 1:
The patent extracts and utilizes the light-dark modulation pattern from security elements, which serves as a sufficient authenticity indicator without requiring full motif recognition. By focusing on the extracted modulation pattern rather than complete image analysis, the system achieves reliable verification with lower optical resolution requirements, reducing device complexity while maintaining measurement precision for authenticity checking
3Ease of operation
If transmission image alone is used for security thread detection, then the ease of operation is improved, but the reliability of authenticity checking deteriorates since motifs are not visible
Solution Approach 1:
The patent merges transmission image detection with remission image detection into a unified authenticity checking process. By combining information from both imaging modes and evaluating the sum of difference values, the system maintains operational simplicity while significantly improving reliability, as the combined approach reveals authenticity characteristics that are not visible in transmission images alone
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables reliable authentication of security elements with reduced sensor resolution requirements and less effort, as the method focuses on intensity modulation along one dimension rather than complex two-dimensional image evaluation, effectively distinguishing genuine from counterfeit security elements.
Implementation Method 1
at least one sensor for detecting electromagnetic radiation remitted and transmitted by the security element
Implementation Method 2
optical elements (e.g. the microlenses) of the security thread, which deflect the incident light depending on the angle of incidence and direct an increased intensity to the detector opposite
Implementation Method 3
the viewer sees an optically variable effect, e.g. an optical movement effect or an enlargement effect, when the security element is moved
Data Source
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Figure 3a~4d
Figure 5a~5d
AI summary
The invention relates to checking the authenticity of the security element of a valuable document. Prior to the invention it was ascertained, surprisingly, that window security threads equipped with microlenses or similar optical elements do not appear dark throughout in the transmission image, but rather have a (mutually opposite) bright-dark modulation in both the transmission and the reflectance images. This opposite bright-dark modulation is checked for the purpose of checking the authenticity of the security element. To that end, the reflectance profile and the transmission profile along the longitudinal direction of the security element are computed with one another pixel by pixel in order to determine a combination profile, and the combination profile obtained by the pixel-by-pixel computation is checked with regard to an intensity modulation along the longitudinal direction of the security element.